Retrievable float valve assembly

Abstract

A retrievable float valve hanger tool assembly provides a hanger sub having a first upper connection for attaching the hanger sub, for example, threadably, to a drill string or work string. A second lower connection means on the sub provides both external and internal threaded (for example) connections, which allow the sub to be connected on its inner threads to a float valve canister and at its external threads to an extension which forms a protective housing about the float valve and its valve canister during operation. The device places the float valve below the joint of the sub and the extension so that an explosive charge can be detonated at the joint allowing easy removal of the float valve from the drill string in the event that the drill pipe becomes stuck. A continuous bore through the assembly allows fluid circulation through the tool in the work string and also allows the explosive charge to be lowered by wireline, for example, to the tool assembly at the appropriate joint. The explosive charge, detonated above the float valve aids in breaking the connection between the hanger sub and extension so that the float valve canister can be removed when the hanger sub and extension are disconnected.

What is claimed as invention is: 
     
       1. A method of disassembling a portion of a drill string containing a float valve comprising the steps of: a. locating a float valve within a lowermost jointed portion of the drill string and a distance below the jointed connection formed in the drill string by the lowermost jointed portion and a connected uppermost jointed portion;   b. forming a suspended connection between the uppermost portion of the drill string and the float valve which is located below the jointed connection adjacent to the lowermost jointed portion;   c. lowering an explosive charge to the jointed connection above the float valve;   d. detonating the explosive charge at the jointed connection above the float valve to loosen the jointed connection;   e. disassembling the uppermost jointed portion and connected float valve from the lowermost jointed portion.   
     
     
       2. The method of claim 1, wherein the step "b" and "a" a canister is provided which is connected at one end portion to the uppermost jointed portion of the drill string and extends downwardly in the drill string bore a distance into the lowermost jointed portion with the float valve being housed within the canister generally below the jointed connection. 
     
     
       3. The method of claim 1, wherein in step "a" the uppermost jointed portion is a section of drill pipe located in the drill string and the lowermost jointed portion is the next lowermost section of drill pipe in the drill string, and the jointed connection is the jointed connection formed between the two sections of drill pipe. 
     
     
       4. The method of claim 1, wherein drill casing is used instead of drill pipe. 
     
     
       5. The method of claim 1, wherein the step "c" the explosive charge is lowered on a wire line. 
     
     
       6. The method of claim 1, wherein in step "c" the explosive charge is a prima cord lowered on a wire line and in step "d" the wire line detonates the explosive charge responsive to actuation at the surface of the drilling operation.